The present invention relates to tightening devices for tightening up or loosening threaded members such as hexagon socket head bolts, hexagon head bolts and nuts, and more particularly to tightening devices suitable for use in tightening up or loosening threaded members for installing, for example, massflow controllers which are to be provided in gas control apparatus for fabricating semiconductors and which must be held highly gastight.
Controllers such as massflow controllers which are provided in such gas control apparatus for fabricating semiconductors and which need to be given high air- or gas-tightness include a member fastened to a base plate with four bolts having a hexagon socket head and arranged on one side of the member, usually with a gasket or like seal disposed between the butting faces. If the bolt tightening torque is too weak, a faulty seal will result, whereas excessive torque deforms the gasket to entail an improper seal, so that each bolt needs to be tightened up with proper torque. Further if one bolt only is tightened with a greater force than the other bolts to result in uneven fastening, the gasket will be deformed to produce a faulty seal. The bolts must therefore be tightened up equivalently. It is also required that the bolts be loosened equivalently so that the gasket will not be deformed greatly to ensure reuse. In installing the massflow controller, accordingly, the bolts are first tightened manually, and one of the four bolts is then tightened with a wrench by a fraction of the required or specified amount of tightening. Next, the second bolt, which is positioned diagonally of the first bolt, is tightened by the same amount, the third bolt adjacent to the second bolt is subsequently tightened by the same amount, the fourth bolt positioned diagonally of the third bolt is tightened by the same amount, and the first bolt is thereafter tightened to repeat the same procedure as above. Thus, the bolts are tightened equivalently by a small amount at a time and eventually screwed up by the specified amount. When to be loosened, the bolts are loosened in a specified order by a small amount at a time.
The following problems are encountered in tightening up or loosening threaded members by the conventional procedure using a wrench for hexagon head bolts.
1. The work of turning the bolts individually by a small amount at a time is cumbersome.
2. The amount the bolt is tightened at a time, if increased, facilitates the tightening work but increases the possibility of deforming the gasket by uneven fastening, hence increased likelihood of making the seal faulty.
3. Although the angle through which the bolt is to be rotated by the wrench after manual tightening is predetermined, the accuracy of the angle of rotation is insufficient because of the manual work involved. This entails the likelihood that the bolt will not be tightened up by the proper amount to cause a fault in the seal.